Processing of photographic color film



Patented Sept. 4, 1951 2,566,664 PROCESSING OF PIIPIIQTOGRAPHIC COLOR Reginald Geoffrey Horner, Ilford, England, as-

- signor to British company Ilford Limited, Ilford, England, a

Application January 2, 1948, Serial No. 365 In Great Britain January 9, 1947 6 Claims.

This invention relates to photography and particularly to processes of photography which include a step involving exposure to light or other radiation of one side only of a photographic material sensitive to such radiation.

Various processes of colour photography have been described in which it is necessary to give a general overall exposure to one side only of the photographic material under conditions uch that none of the exposing light penetrates to the other side of the material. The direct penetration of the exposing light through the film is usually prevented by the provision of a so-called barrier" layer in the material, this layer absorbing light of the wavelengths used for the exposure. For example, a typical colour photographic material may consist of the following layers in order:

(a) A transparent support layer (12) A red-sensitive silver halide emulsion layer A green-sensitive silver halide emulsion layer (d) A yellow filter layer (e) A blue-sensitive silver halide emulsion layer.

On exposure of such a material in a camera, with layer e nearest to the lens, blue, green and red records of the subject photographed are produced in layers e, c and b respectively. On development these are obtained as negative records. If now the individual layers e, c and b are selectively re-exposed to render the residual silver halide developable and are then selectively developed under conditions which yield in layer e a yellow dyestufi, in layer 0 a magenta dyestuif and in layer 1) a cyan dyestuff, the dyestuii being formed in situ with the developed silver images, there is obtained, after removal of the silver and residual silver salts, a positive colour record of the original subject photographed. In order to render the residual silver halide in layer e developable, it may be re-exposed to blue light. This light must not, however, penerate to layers 0 and b and its penetration may be prevented by arranging that there is a deep yellow filter between layers 0 and e. Similarly, if there is a deep yellow filter between layers b and 0, layer b may be re-exposed to blue light (entering through layer a without affecting layers 0 and e).

There are innumerable variations possible in the processing technique in which lights of colours other than blue or radiation other than light, e. g. ultra-violet or infra-red rays, are used appropriate barrier layers being provided.

The practical aspects of the re-exposure step are, however, somewhat difiicult. It is found that there is a tendency for the re-exposure to be uneven, especially if the photographic material is still wet from previous processing steps.

This may be overcome by effecting the re-exposure with the photographic'material immersed in water (or other inert liquid). Conveniently this may be done by arranging that the film passes through a tank of water close to a glass window in the side, bottom or top of the tank.

It has been found, however, that using this technique there is a considerable difficulty in preventing any of the exposure light from passing the edges of the film and being reflected back on to the surface which it is not intended to expose. The difiiculty cannot be entirely overcome by using a tank with walls of low refiecting power for, although special designs for absorbing the light, such a multiple reflection by black glass mirrors, are possible, the water itself scatters the light back, especially if itcontai'ns dust particles or other suspended matter. Nor is it suflicient to arrange for the edge of the film to run in a channel groove and so prevent direct light entering the tank, since the inside surfaces of the channel themselves tend 'to reflect the exposing light. 7

According to the present invention a method of exposing one side only of a radiation-sensitive material comprises directing radiation to which the material is sensitive on to one side only of the material while the material is immersed in a liquid which absorbs the radiation employed, the material being positioned so that the depth of liquid between the source of the radiation and. the material is small compared with the depth of liquid in any direction behind the material. The exposing radiation is therefore not much absorbed by the liquid before I'BaCh! in the material, but stray radiation passing the edges of the material i sufiiciently absorbed to reduce back scattering within the liquid to negligible proportions, and completely absorbed beforeit .can reach the back pf the material after.

3 reflection from any part of the walls of the tank lying behind the plane of the material.

Preferably the liquid is contained in a tank provided with a window in the side, top or bottom, the material bein arranged to be close to the window and being exposed by radiation entering through the window. If the window is at the top of the tank, the liquid should preferably wholly fill the tank so that there is not a free liquid surface between the source of radiation and the material. It, this way unevennes of exposure due to ripples on the surface of the liquid may be avoided. u The invention is of especial value in the re exposure of reversal type colour film where it is" required to re-expose a layer nearer to the exposing source without afiecting a layermore remote from the exposing source. Generally such re-exposure i made by means of blue light and in such a case the liquid may be water containing a blue-absorbing (i. e. yellow) dues'tuff. If the exposing source is white light or coloured light other than blue, or ultra-violet or infra red rays, the liquid should be appropriately absorptive'of such radiation; p g

It is preferred that theliquidshould be contained in a vessel of which the internal walls are also absorptive of the radiation to be used for the exposure, and for most-purposes an internally blackened tank is suitable.

The following specific example illustrates the invention:

Example A photographic consisting ofa transparent support bearing on one side two superimposed sliver halide, photographic emulsions each sensitive to blue light and between them a deep yellow filter layer was suspended me tank of water in a position parallel to and about half an inch from a glass window in the side of" the tank. The tank was internally blackened'and measured 16 inches long by 12 inches wide by 37 inches deep. The window was in the smaller side so that a depth of inchesofwater wasprovided behind the film. For the purposes' of this example the width of the film was about half the width of the window so that avery considerable amount of theex'po'sing light'pa'ss'edby the edges of the film eta into the tank. 11 6 exposing light was used aii'dthe extent of the" exposure adjusted to about times that necessary to render fully developable the snterhendeef the emulsion nearer to the exposing source. The yellow filter layer was of sufiicient density to prevent any direct exposure of the silver halide of the other: emulsion layer, but nevertheless a dye image density of 1.3 was obtained in this layer owing to the exposure received byback-refiected light.

The addition to the water in the tank of a small amount of the dyestuff Tartrazine (Colour Index No. 640) in the proportion of 2 parts in 1 million parts of water by weight'was sufiicient to eliminate completely this back-exposure.

In practice about of the above exposure to blue light would be given, and precautions taken tomask' the window down to the size of the film would reduce the amount of exposing light passing the edges of the film by at least 10 times. A concentration of Tartrazine of 2 parts in a million would therefore give a factor of safety of at least 100, and a much smaller quantity of dye would be sufiicient to prevent the fogging of the second emulsion layer, e. g. l'partof dye in'10' million parts of water.

The invention is illustrated by the accompany lng drawing which shows exposing rays from a source entering the transparent window of a tank wholly filled with dyed liquid absorbtive of the exposing rays. A very short distance below the window is the film to be exposed, and as shown the rays penetrate the film as far as the filter layer. The drawing shows the track of one exposing ray which passes the edge of the film and is progressively absorbed by the dyed liquid. It shown as reflected from the wall and bottom of the tank back to the underside of the film, and the relative intensity of the rays striking the film from the topand those striking the film from below, ignoring light losses by reflection at the surfaces of the tank, will be inversely as the relative lengths of the free paths of the rays from the window ;to theltop of the film and from the window to the bottom of the film. On the dimensions of the drawing this will be about 100 to 1.

What I claim is:

1. In the development to colour of reversal type multilayer colour film wherein it is required to re-expose an incident light-sensitive layer without aifecting a Second morerem te, layerthat is also sensitive to the incident radiation, and which is separated from said first-mentioned layer by afilter layer that is highly absorptive of said incident radiation, the method of preventing re-exposure radiation that passes the" edge of the filth from fogging" said secon'd, more remote, layer by directing exposing radiation on said incident layer while the film is immersed in a coloured liquid containing a dye that is highly absorptive'of the radiation employed, the film being pqsitioned so that the depth of the coloured liquid between the source of radiation and thefilm is small compared with the depth of liquid in any directionbehind the film.

2. In a: method of exposing one'incidentjight; sensitive layer of a photographic element having at least one other differentiallylight-sensitive layer that is separated from said first-men tioned layer by a filter layer that is highly abser' iveer the incident radiation, the step of preventing the incident radiation that passes the edge of the photographic element from affecting said other d ifiereiitially light-sensitive layer by directing light radiations to one surface of the incident layer, while said photographic element is ifr'niners'ediin, a coloured liquid dntaiil ng a dye that s highly absorptive of the light radiations employed, the photographic element being positioned so that the depth of, liqi id etwee hesetreeer radiation and the incidentlayeris small tempe ed with the epth; of liq iii any'direction behind the photograph ic element. v v

3. A' according to claim 2 wherein the liquid i's' cont s ained in a vessel the internal walls of whichare also absorptive of said radiation. ei m ethod according to claim 2 wherein there is no i ree surface ofliguid between the source of radiation and the radiation-sensitive a a .5- 1 ameth of xposi n i c li tsensitivelayer of a photographic film element having three differentially light-sensitive silver halide layers and a blue light absorbing filter, layer disposed: between the incident layer and the adjacentv light-sensitive layer, the step of preventing the incident radiation ,that passes the edge ofthe'filn'i element from affecting other than said incident light-sensitivelayer by directing light radiations to one surface of the incident layer while said film element is immersed in a coloured liquid containing a dye that is highly absorptive of the light radiations employed, the film element being positioned so that the depth of liquid between the source of radiation and the incident layer is small compared with the depth of liquid in any direction behind the film element.

6. A method as set forth in claim 5 wherein blue light radiations are directed to the incident layer and the film element is immersed in a yellow-coloured liquid.

REGINALD GEOFFREY HORNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 409,618 Spiro Aug. 20, 1889 437,629 Spiro Sept. 30, 1890 1,762,936 Seymour June 10, 1930 2,066,102 Eggert et a1. Dec. 29, 1936 2,232,056 Eggert et a1. Feb. 18. 1941 2,330,796 Bennes Oct. 5, 1943 

1. IN THE DEVELOPMENT TO COLOUR OF REVERSAL TYPE MULTILAYER COLOUR FILM WHEREIN IT IS REQUIRED TO RE-EXPOSE AND INCIDENT LIGHT-SENSITIVE LAYER WITHOUT AFFECTING A SECOND, MORE REMOTE, LAYER THAT IS ALSO SENSITIVE TO THE INCIDENT RADIATION, AND WHICH IS SEPARATED FROM SAID FIRST-MENTIONED LAYER BY A FILTER LAYER THAT IS HIGHLY ABSORPTIVE OF SAID INCIDENT RADIATION, THE METHOD OF PREVENTING RE-EXPOSURE RADIATION THAT PASSES THE EDGE F THE FILM FROM FOGGING SAID SECOND, MORE REMOTE, LAYER BY DIRECTING EXPOSING RADIATION ON SAID INCIDENT LAYER WHILE THE FILM IS IMMERSED IN A COLOURED LIQUID CONTAINING A DYE THAT IS HIGHLY ABSORPTIVE OF THE RADIATION EMPLOYED, THE FILM BEING POSITIONED SO THAT THE DEPTH OF THE COLOURED LIQUID BETWEEN THE SOURCE OF RADIATION AND THE FILM IS SMALL COMPARED WITH THE DEPTH OF LIQUID IN ANY DIRECTION BEHIND THE FILM. 